Transition metal-based nanomaterials exhibit promising potential as highly active and low-cost electrocatalysts for alkaline water splitting, which can be achieved via elaborating compositional modulation and structural manipulation. This, however, normally involves multiple or even complex synthetic procedures. Herein, we report a simple one-step sulfidation of FeMnZn multi-metal skeletons for the preparation of highly efficient electrocatalysts. The incorporation of Mn and Zn induced a hierarchical nano/micro sheet-to-sheet morphology supported on an open porous skeleton (FeMnZn/Mn-FeS, FMZS2), which not only facilitates electron/ion transport but also expands the accessible surface. Meanwhile, Mn is introduced to optimize the adsorption/desorption ability of intermediates on the S sites in FeS. The resultant effect leads to remarkable electrocatalytic performance with good durability. Notably, the optimized FMZS2 delivers 20 mA cm⁻² at a low overpotential of 118 mV for the HER and 100 mA cm⁻² at an overpotential of 390 mV for the OER, outperforming Pt/C and IrO₂ catalysts, respectively. Moreover, the assembled alkaline electrolyzer also has good overall water splitting capability, which is better than that of the noble metal ones.